Features

• For 850 nm or 1300 nm Center Wavelengths
• Ideal for Swept Source Output Frequency Monitoring
• Balanced Detection Output
• Low Insertion Loss: <3 dB
• Flat Wavelength Response
• Integrated Signal Detection for Power Monitor and k-Clock Signals
• Interferometer Power Supply Included

Thorlabs' Mach-Zehnder interferometer clock box subassemblies are designed to be used inside a swept source OCT system with a central wavelength of either 850 nm or 1300 nm. The internal fiber couplers are optimized for flat wavelength responses and coupling losses that have a very low polarization dependence, which make the output signals independent of input polarization changes. The clock box contains two detectors, providing a power monitor signal and a k-clock signal that monitors the output frequency of the swept source. Both outputs have a 200 MHz bandwidth, and the k-clock uses a balanced detection scheme to maximize rejection of common mode noise.

Although originally designed for OCT systems, this clock can also be used for other synchronization applications.
For more details on the clock, please see the Operating Principles Tab.

Note: Custom models are available with a choice of free spectral range and wavelength. Please contact tech support for more information.

Operating Principles

Rapidly swept laser sources typically use sinusoidal tuning elements to achieve the very fast optical frequency sweep speeds required for OCT imaging applications. Hence, accurate and reliable re-calibration of the OCT signal is required so that the final data points are equidistant in frequency. The Thorlabs swept source laser features a built-in Mach-Zehnder Interferometer (MZI) with balanced detector output that can be used for just this purpose. A frequency clock is derived from the zero crossings of the MZI interference fringe signal; these zero crossings are equally spaced in optical frequency (k-space). While this clock is intended for OCT applications, it can also be used in other synchronization applications.

Figure 1: MZI Clock Signal

The schematic of the system is shown in figure 2. below. An internally fiber network is used to tap 5% of the input light to generate Power Monitor and k-clock signals. The remaining light is transmitted to the Output pigtail. Specially designed couplers are used to achieve a flat wavelength response for both the transmitted and the Power Monitor signal. (see figures 3 and 4 below). Both signals of the MZI are detected by an ultra-low noise amplified balanced photo detector.

Figure 2: Schematic of MZI Series Clock Box

Figure 3: Coupling Ratio for INT-MZI-1300 from Input to Output

Figure 4: Coupling Ratio for INT-MZI-1300 from Input to Power Monitor